Flight control system employing complementary filter

Abstract

Strake, flap and canard control surfaces of an aircraft are driven by an error signal which is comprised of a pilot stick command signal and feedback components including measured vertical acceleration and pitch rate of the aircraft and a third feedback component derived from a complementary filter. The filter has a high-pass filter section which operates upon canard position data and a low-pass filter section which operates upon pitch rate. A summation of the signals passing both filtering sections is summed with the vertical acceleration and pitch rate feedback signals to form a combined feedback signal.

I claim: 
     
       1. In a flight control system for reducing a multi-control surface aircraft wherein an error signal is formed from signal components including a pilot stick signal and a composite feedback signal, the system comprising: means for sensing vertical acceleration of an aircraft and generating a signal corresponding thereto;   means for sensing pitch rate of an aircraft and generating a signal corresponding thereto;   a complementary filter having (a) means for high-pass filtering a signal generated from a position sensor connected to one of the control surfaces;   (b) means for low-pass filtering the signal generated from the position sensor connected to the control surface;   (c) means for summing the low and high pass filtered signals;     means for combining the stick signal, vertical acceleration, pitch rate, and summed filtered signals to form the error signal; and   means for connecting the error signal to actuators for each of the multi-control surfaces.   
     
     
       2. The structure set forth in claim 1 wherein said control surface having a position sensor connected thereto is a canard. 
     
     
       3. The structure set forth in claim 2 wherein the high-pass filtering means comprises means for differentiating the sensor signal from the canard with a time constant selected to maximize stability margin for the aircraft. 
     
     
       4. The structure set forth in claim 2 wherein the low-pass filtering means comprises: means for estimating a value of pitch rate from a two-point estimate; and   means connected to the two-point estimating means for integrating the estimated value of pitch rate with a time constant selected to maximize the stability margin for the aircraft.   
     
     
       5. The structure set forth in claim 4 wherein the high-pass filtering means comprises means for differentiating the sensor signal from the canard with a time constant selected to maximize the stability margin for the aircraft. 
     
     
       6. A flight control method for use with a multi-control aircraft comprising the steps: sensing vertical acceleration of an aircraft and generating a signal corresponding thereto;   sensing pitch rate of an aircraft and generating a signal corresponding thereto;   high-pass filtering a signal generated from a position sensor connected to one of the aircraft control surfaces;   low-pass filtering the signal generated from the position sensor connected to the control surfaces;   summing the filtered signals;   combining the stick signal, vertical acceleration, pitch rate and summed filtered signals to form the error signal; and   connecting the error signal to actuators for each of the multi-control surfaces.   
     
     
       7. The method set forth in claim 6 wherein the high-pass filtering further comprises the step of differentiating the sensor signal from a control surface with a time constant selected to maximize stability margin for the aircraft. 
     
     
       8. The method set forth in claim 7 wherein the low-pass filtering further comprises the steps: estimating a value of pitch rate from a two-point estimate; and integrating the estimated pitch rate with a time constant selected to maximize the stability margin for the aircraft.